1. Field of the Invention
This invention relates to a guide bushing for guiding a drill string of a blast hole drill, and more particularly to such a guide bushing that is mountable in the deck or table of the blast hole drill.
2. Description of the Prior Art
Heretofore, guide bushings of the foregoing character have been available to the industry. In one type, such guide bushings have been made entirely of metal and, hence, have been extremely noisy in operation and have transmitted excessive vibrations to the blast hole drill in which they have been installed. Although relatively inexpensive, such metal bushings have not had long service life, and have tended to rapidly wear the drill string.
U.S. Pat. No. 3,951,470 to McLean discloses a guide bushing for a blast hole drill that improves upon the prior metal bushing. This patented bushing employs ball bearings. It is much more costly than the prior metal bushing, yet it is not very quiet in operation, and is understood to have a relatively short service life.